Stent and Stent Retrieval System and a Method of Pulling a Stent Into a Tubular Member

ABSTRACT

A stent has an engagement member ( 9 ). A stent retrieval system has a tubular member ( 13 ) and a retrieval member ( 14 ) with an engagement means ( 15 ). The engagement member is attached to an end row of cells of the tubular stent body ( 1 ). The cells in one annular row of cells are interconnected with the subsequent row of similarly oriented cells ( 2   a ) at areas of interconnection ( 7 ) which in the subsequent annular row of cells are circumferentially offset with respect to the connections ( 8 ) between the cells in said subsequent annular row of cells.

The present invention relates in a first aspect to a stent and a stentretrieval system, said retrieval system comprising a tubular member witha lumen terminating in a distal end opening, and a retrieval member withat least one engagement means, the tubular member and the retrievalmember being mutually axially displaceable while the retrieval memberextends in said lumen of the tubular member, said stent comprising atleast one engagement member to which said at least one engagement meanscan engage and a tubular body of a plurality of annular rows of cellsthat are interconnected and located one after the other in the axialdirection of the tubular body, the cells in one annular row of cellsbeing interconnected with the subsequent row of similarly oriented cellsat areas of interconnection which in said sub-sequent annular row ofcells are circumferentially offset with respect to the connectionsbetween the cells in said subsequent annular row of cells.

Such a stent and a stent retrieval system is known from WO 2004/008991disclosing a stent having in one end larger cells that are not arrangedin annular rows but instead in rows extending over only one side of thestent. The cells in this end structure have been given a more coarsestructure, and in the end row there is only a single cell into which anengagement member can engage.

U.S. Pat. No. 5,643,309 describes a stent provided with a number ofinward projecting hooks at a distance from each end of the stent. Thestent retrieval system comprises an outer sheath and a tubular memberwith an engagement ring fixed to carrier legs on the outside of thetubular member, and an inner retrieval member provided displaceably inthe tubular member. The retrieval member is also provided with anengagement ring fixed to carrier legs on the outside of the member. Whenthe stent is to be removed from a vascular site, the sheath isintroduced into the stent, and the tubular member and the retrievalmember are both advanced out of the sheath and tubular member,respectively, so that both engagement rings are allowed to expand withinthe stent. The two engagement rings are brought into engagement with thetwo sets of hooks on the stent, and then the tubular member and theretrieval member are moved in opposite directions so that the stent ispulled out to a longer length by the action of the rings on the hooks.Due to the elongation of the stent its diameter is reduced to such anextent that the stent is released from the vascular wall, and then thestent is pulled out. The system is complicated and difficult to use.

EP 0 829 242 A1 and US 2002 0120277 A1 both describe a stent retrievalsystem comprising a tubular member with a lumen terminating in a distalend opening, and a retrieval member with a plurality of engagement meansshaped as tines with outward open hooks that after introduction to aposition inside the stent can be moved radially outwards into the wiremesh of the stent. When the retrieval member is withdrawn the hooksengage in the wire mesh and pulls the stent out to a longer length. Asthe stent is pulled longer its diameter is reduced. The combined pullingaction and diameter reduction acts to tear the stent loose from thevascular wall.

In U.S. Pat. No. 5,910,144 a plurality of gripper elements can be movedto the position of a stent and be allowed to radially spread out to alarger diameter than the stent diameter so that the gripper elements canbe pushed in on the outside of the stent. Then the grippers are movedradially together so that the stent is compressed to a smaller diameterand can be pulled out.

It is in the first aspect of the present invention an object of theinvention to obtain a stent and a stent retrieval system providing amore secure retrieval of the stent.

To meet this object the stent and stent retrieval system ischaracterized in that the end row of cells is an annular row of cellscomprising first cell sides forming at least one circumferentiallyclosed loop in which the individual cell has an attachment point, thatsaid at least one engagement member comprises at least three tie membersthat are mutually connected at a junction and extend individually fromthe junction to the attachment point of an associated cell, and that theattachment points in the annular end row of cells are circumferentiallyoffset with respect to the connections or areas of interconnection atthe end of the tubular body between the cells in said end row.

The at least three tie members in the engagement member provide a firmand suitably distributed grip in the first row of cells at the end ofthe tubular body so that the cells are folded in a symmetrical manner.By attaching the engagement member to the annular end row of cells atpoints that are circumferentially offset with respect to the connectionsbetween the cells in the row, a pulling action in the engagement memberwill cause deformation of the cell sides extending between theindividual attachment point and the adjacent connections between cells.The initial pull draws the engagement member towards the tubular memberand into abutment with the distal end opening thereof, and duringfurther pulling the engagement member is pulled into the lumen of thetubular member and the end row of cells is brought to abutment with therim of the opening. As the engagement member is pulled into the lumen itacts on the end row of cells and cause some deformation thereof. Asthese deformations act locally and only to the end side of the annularrow of cells, that row of cells will radially collapse to a smallerdiameter at the end side, but remain at almost the initial diameter atthe opposite side of the annular row. It is an advantage that the tiemembers extend individually to the attachment points because this on theone hand minimizes any obstructing effect from the tie members on theflow in the vascular vessel as any filtering effect or the like on theflow in the vessel is highly undesired, which could easily have occurredhad the tie members been inter-connected in between the junction and theattachment points, and on the other hand any pull at the junction isautomatically evenly balanced between the tie members when they extendindividually to the attachment points.

The collapsed end side can be drawn radially down towards and into thedistal end opening by pulling in the engagement member. As this is done,the cell sides in the end row of cells are turned and/or bend inwards inan angle that increases as the end side is pulled down to a smallerdiameter. This pattern of movement of cell sides is very advantageous,especially when the stent is to be removed from a vascular site where ithas been temporarily positioned for a desired period of time, becauseonly minimum damage is done to the vascular wall.

When a stent is placed in a vessel, e.g. a blood vessel, tissue willwithin few days be formed around the stent material. Such ingrowth oftissue makes the stent become an integral part of the vascular wall. Theingrowth results in a layer of tissue, called intima, on the inside ofthe stent. If a stent is removed by using the prior art techniques ofstent removal where the diameter of the stent is reduced by pulling thewhole stent out to a longer length the tearing loose from the intimaacts along a large area of the vascular wall, and the risks of damagingthe vascular wall are high. If the vessel is weak, which is often thecase in places where a stent is utilized, there is even a quite highrisk of tearing the vessel apart when the stent is removed. With thepre-sent invention it has been recognized that the tearing apart can becaused by an axially directed pull in the stent in conjunction with aradial contraction that acts along a substantial length of the stent.

The stent according to the present invention is not subjected to anysubstantial axial pull during removal. The pulling in the engagementmember only needs to be sufficient to pull down one side of one annularrow of cells. When this pulling is effected the vascular wall remainssupported by all remaining cells in the annular rows that have not yetbeen moved into the tubular member. The stent is thus kept axiallystationary with respect to the parts of the vascular wall being incontact with the stent. The annular row of cells which is in the processof being pulled radially down into the tubular member is released in agentle manner from the vascular wall. This is so, because only one sideof the row is initially moved free of the vascular wall, and then thecell material is gradually moved free in direction of the other side ofthe row due to the cell material turning or bending inwards in thevessel. When one side of the annular row has been moved into the distalend opening, the tubular member is pushed forwards in direction of theother side of the annular row located at the subsequent annular row ofcells.

During this pushing of the tubular member the cell material enters thedistal end opening and then the other side of the annular row is pulleddown to a smaller diameter and in doing so the cell material is movedradially inwards and out of the vascular wall. Then the process isrepeated with the subsequent annular rows of cells. The areas ofinterconnection between one row and the subsequent row are offset in thecircumferential direction with respect to the connections between thecells in the subsequent row. A pulling action in interconnections willcause deformation of the cell sides extending between the individualattachment point and the adjacent connections between cells. As thesedeformations act locally and only to the end side of the annular row ofcells that row of cells will radially collapse to a smaller diameter atthe end side, but remain at almost the initial diameter at the oppositeside of the annular row. Then the tubular member can be pushed forwardto the next annular row. The procedure is repeated until the stent hasbeen placed completely within the tubular member, and then the retrievalsystem is withdrawn from the vascular system.

From the above explanation it follows that the cell material of thestent is released from the vascular wall by effecting radially actinglocal pulls in the cell material anchored in the vascular wall so thatthe cell sides are moved towards the centre line of the tubular bodyduring the release from the vascular wall, and the radially directedpulling forces act symmetrically on the tubular body in thecircumferential direction. The pulling forces furthermore only act onthe annular row of cells that are in the process of collapse. The cellsin the tubular body located more than one annular row of cells away fromthe collapsing cells are consequently unaffected by the forces used tocollapse cells.

Also the annular end row of cells is released from the vascular wall bymainly radially acting forces caused by the engagement member beingdrawn in through the distal end opening of the tubular member. The tiemembers collectively and simultaneously act on the attachment points inall cells in the end row when the engagement member is moved into thelumen of the tubular member. The tie members extend directly from thecommon junction to their individual attachment point on the cell towhich the individual tie member is connected.

The stent retrieval system can also be utilized to position a stent inthe tubular member from an unloaded stent condition before the stent isintroduced into a patient. The retrieval system can in other words beused as a system for loading a stent into a tubular member, e.g. anintroducer system.

In an embodiment the individual attachment point is circumferentiallylocated approximately at the middle between the two adjacentconnections. With such a location the cells in the end row will collapseevenly about the attachment points. It is of course also possible, butnot preferred, to position the attachment points in an asymmetric mannerwith respect to the adjacent connections.

In another embodiment the individual area of interconnection to asubsequent annular row is circumferentially located approximately at themiddle between the two adjacent connections. With this location thecells in the subsequent row will collapse evenly about the areas ofinterconnection. It is of course also possible, but not preferred, toposition the areas of interconnection in an asymmetric manner withrespect to the adjacent connections.

In a preferred embodiment the first cell sides extending from theindividual attachment point form mutually on the side of the attachmentpoint an angle (δ) of less than 176°. As a consequence of this designthe first cell sides have to raised through the angle of 180° before endcells in the end row begin to collapse. During this movement thediameter of the end of the tubular body is slightly increased and thiscauses some resistance which allow the engagement member to be drawnpartly into the distal end opening and said end opening to be pushedcloser towards the end row so that the tie members are oriented moreradially, or in mainly radial directions, in areas adjacent theattachment points before the cells in the end row are brought tocollapse. This design enhances the effect of causing radial directedpulls in the cell sides during release of the cell sides from thevascular wall.

In an embodiment the same principle is utilized in the internal rows ofcells in the tubular body, in that the individual annular rows of cellslocated within the tubular body the first cell sides form at least onecircumferentially closed loop in which the first cell sides extendingfrom the individual area of interconnection form mutually on the sidefacing the end row with the attachment points an angle (δ) of less than176°. This embodiment can be used either in conjunction with the justmentioned design of the annular end row or on its own if the increasedresistance against pulling down the annular end row is consideredundesirable. In any case, in this embodiment the second cell sides willduring their being pulled into the tubular member act as described abovein connection with the tie members so that they will be oriented moreradially, or in mainly radial directions, in vicinity of the areasinterconnection just before the cells in the subsequent row are broughtto collapse.

In a preferred embodiment the first cell sides in the individual annularrow of cells form at least one circumferentially closed loop in whichsaid first cell sides constituting the loop extend in directions formingangles in the range from 60° to 120° with the axial direction of thetubular body, when the tubular body is in an unloaded state. The closedloop provides the stent with high stiffness against radial compressionand thus good properties for keeping a vessel patent, even at locationswhere the vessel exhibits a bend, but more importantly the closed loophas a high ability of maintaining its initial diameter when a local pullis performed in adjacent cell material. If the angle deviates well above30° from 90° the tendency of maintaining the initial diameter can becomefeeble. It is preferred that the angular range is in the range from 70°to 110°, because the annular row of cell will then only to a smallextent obtain a larger diameter when the first cell sides are pulled indirection of the distal opening. If the angular range is limited to therange from 75° to 105° the pull in the engagement member can be keptmore constant.

In an embodiment second cell sides in the individual annular row ofcells interconnect the circumferentially closed loops and extend atleast along part of their length in directions forming angles in therange from 20° to 70° with the axial direction of the tubular body, whenthe tubular body is in an unloaded state. The flexibility of the secondcell sides and the width of the individual annular row are comparativelywell balanced when the angles are within the stated range. The range ispreferably from 30° to 60°.

Preferably, said first cell sides extend substantially in a radial planeat the distal end opening of the tubular member, when said second cellsides in the adjacent annular row of cells have been pulled in throughthe distal end opening to extend from said distal end opening and intothe tubular member. When the first cell sides can turn or flex to extendin or approximately in a radial plane when the second cell sides havebeen pulled through the distal end opening then the tubular body canmaintain its initial diameter for as long time as possible.

It is preferred that the outer diameter of the subsequent loop outsidethe tubular member remains mainly unaffected while a loop is pulled intothe distal end opening. As the subsequent loop is not affected thevascular wall at the subsequent loop is neither affected.

The junction of the engagement member is preferably located at thelongitudinal central axis of the tubular body. By locating the junctionat the central axis establishment of the engagement between theengagement means and the engagement member is more easily accomplished.The pull in the engagement member is also more evenly distributed to theattachment points when the junction is located at the central axis wherethe junction is symmetrically positioned with respect to the end row ofcells.

In a most preferred embodiment the tie members a length so that thejunction is located at least 0.5×W away from the annular end row ofcells at the end of the tubular body, W being the width in the axialdirection of the annular row of cells. By positioning the junction atsuch a distance from the end loop, this loop is more easily subjected tomainly radially acting forces when the junction is pulled in through thedistal end opening because the length of the tie members assists to thebending of the tie members in the area in front of the distal endopening before the tie members are pulled completely into the lumen. Thebent tie members will gradually pull the attachment points radiallyinwards as the tubular member is pushed in direction of the end loop,until the attachment points are located at the distal end opening with amutual radial separation corresponding to the inner diameter of thelumen in the tubular member. This embodiment can be utilized on its ownor in conjunction with the above mentioned embodiment where the firstcell sides form an angle of less than 180° on the side facing theattachment point to which the first cell sides are connected.

In an embodiment the at least one engagement member comprises magneticmaterial. The engagement member can e.g. be of a ferromagnetic materialwhich can attract a magnet, or it can be a magnet with a polarity facingin a certain direction, such as in the axial direction or the radialdirection of the tubular body. In case the magnetic material has apolarity, this polarity can be opposite to the polarity of a magneticmaterial located on the engagement means so that the engagement means isattracted to the engagement member. Such an attraction effect can alsobe obtained with a magnet on one of the engagement member and theengagement means, when the other of the two parts is of a ferromagneticmaterial. The purpose of the magnetic materials is to facilitate theestablishment of the engagement grip in the engagement member when thisis located inside a vessel.

The inner lumen of the tubular member can have a diameter in the rangefrom 20% to 80%, preferably from 30% to 60%, of the outer diameter ofthe tubular body in the unloaded state of the tubular body. Although itis possible to use a tubular member with a lumen of less than 20% of theouter diameter of the tubular body, there is not obtained any advantageby this, but to the contrary the lumen gets so diminutive that is may bemore difficult to receive the tubular body in the lumen. The upper limitof 80% is sufficient to obtain full release of the stent from thetubular wall. The preferred range from 30% to 60% entails the advantagesof providing more space in the lumen and a comparatively small outerdiameter of the tubular member, thus facilitating the introduction ofthe stent retrieval system through the vascular system to the stentposition.

In an embodiment the tubular body is provided with at least oneadditional means selected from the group consisting of a medicallyactive substance, a bioactive factor inhibiting proliferation of a tumorcell, a bioactive substance, a bioactive agent, a drug, and a coatinglayer for controlled release of one or more of a bioactive material, amedically active substance or a bioactive factor. The bioactivesubstance or agent can e.g. be of a kind that reduces negativeinfluences from the stent on the vascular wall or of a kind thatenhances the effects of placing a stent in the vascular system.Alternatively the stent can be utilized as a carrier for introducing thesaid substance, agent, factor or drug to a vascular site where localizedrelease of said substance, agent, factor or drug is desired. The stentis kept in place in the vascular system in the period required forobtaining the desired release of the substance, agent, factor or drug atthe vascular site, and then the stent is removed by using the stentretrieval system. The stent retrieval system is in particularadvantageous for such use, because of the very gentle removal procedurewhere the stent material is released from the vascular wall without oralmost without subjecting the vascular wall to substantial forcesdirected in the axial direction of the tubular body. The annular rows ofcells are individually released from the vascular wall by the mainlyradial collapse of the rows. The vascular wall is quite often very weakat the locations where local release of drugs etc. is required. Theweakening can e.g. be caused by the presence of tumor cells in vicinityof the vascular wall. Because of the gentle removal of the stent therisks of damaging the vascular wall by the removal are reduced to aminimum. It is consequently possible to treat even quite weak vascularsites with a temporary stent, which has hitherto not been possible.

In an embodiment said additional means has a predetermined active periodin the range from three days to one month, preferably from 5 to 14 days.Ingrowth of an intima layer on the inside of the stent will increasewith the duration of the placement. Due to the gentle removal of thestent it becomes possible to treat the vascular site for a longerperiod, such as up to one month, and yet remove the stent withoutinflicting intolerable damage to the vascular site.

It is possible to provide the tubular body with a tubular covering, suchas a weave of graft material. The covering can serve to provide thestent with a large surface area, which can be an advantage, inter aliain cases where larger amounts of a drug or a bioactive substance oragent needs to be introduced to the vascular site. The covering can alsobe required in order to obtain temporarily closure of a branch vessel,an aneurysm or another vascular malformation.

In another aspect the present invention relates to a method of pulling astent into a tubular member, the stent comprising at least oneengagement member and a tubular body having a plurality of annular rowsof cells that are interconnected and located one after the other in theaxial direction of the tubular body, where at least one engagement meansgrips the at least one engagement member and pulls it through a distalend opening of the tubular member and into an inner lumen of saidtubular member, said annular rows of cells having an initial diameterwhich is larger than the diameter of said inner lumen. Such a method isknown from the abovementioned U.S. Pat. No. 5,643,309.

In relation to this second aspect the object of the invention is to loada stent into a tubular member in a simple manner and without use ofcomplicated additional equipment.

With a view to this the method is characterized by pulling said at leastone engagement member into and along the lumen of the tubular member andpushing the tubular member towards the tubular body, whereby the annularrows of cells are brought towards the end opening and are collapsedone-by-one at the end opening to a state with a radially reduceddiameter, while the annular rows of cells maintain their initialdiameter at least until they are within one row from said end opening.

The forces required to move the stent into the tubular member are quitelow because the forces act mainly on the annular row of cells positionedimmediately in front of the tubular opening. When cell sides in theannular row are pulled against the rim of the opening these cell sidesdeflect under the action of the rim to be oriented towards the innerlumen in the tubular member. During the continued pull in the engagementmember the cell sides re-orient themselves at the radially reduceddiameter corresponding to the inner lumen in the tubular member. Thenthe tubular member can be pushed towards the stent so that the rim ofthe end opening is moved towards the other side of the annular row ofcells. During this movement the inner cell sides in the annular row arebrought into the lumen, and because of the smaller diameter of the lumenthese inner cell sides effect an increasingly strong radially directedpull in the cell sides at the opposite side of the annular row of cellsso that these cell sides come to extend from the next annular row ofcells at the initial diameter of the stent and inwards to radially moreclosely spaced locations at the end of the inner lumen of the tubularmember. Then the procedure can be repeated with the next annular row ofcells.

As there is no need for using complicated equipment in order to load thestent into the tubular member by the method of the present invention theloading can be performed shortly before the stent is to be used. Thisprovides the substantial advantage of allowing a preparation of thestent with a coating having active properties of time-limited effect. Ifthe active property of the coating only lasts for e.g. 7 or 14 days thenthe effects are lost during shelving of manufactured stents. By applyingthe coating to the stent shortly before the stent is to be used, and byloading the coated stent into the tubular member in the abovementionedmanner, the stent is ready for use without any decay of the activeproperty.

The invention will be explained in detail in the following by means ofexamples of embodiments with reference to the schematic drawing, inwhich

FIG. 1 is a plane view to illustrate the cell structure used in anembodiment of a tubular body of a stent according to the invention,

FIG. 2 depicts a side view of the stent having a cell structure asillustrated in FIG. 1,

FIG. 3 a to 3 d show side views of sequential steps of the stent of FIG.2 being pulled into a tubular member by use of a retrieval system,

FIG. 4 shows a cross section along the line IV-IV of FIG. 3 e viewedfrom the left side of FIG. 3 e, and

FIG. 5 shows a plane view corresponding to the view of FIG. 1 of anotherembodiment of a stent according to the invention made by laser cuttingor etching in a tubular member.

FIGS. 1 and 2 illustrate the structure of a stent according to theinvention, the stent being in an unloaded state. The stent is made up ofwires that are bent or wound in a pattern to form a tubular body 1, seeFIG. 2. For the sake of ease the cell pattern is illustrated in FIG. 1in a cut up, unfolded state of the stent. The pattern is formed byannular rows of arrow-head-shaped or heart-shaped cells 2 a, the rowsbeing interconnected and arranged one after the other in the axialdirection A of the tubular body 1. The annular rows of cells 2 a havethe same orientation in the tubular body. In between these rows of cellsthere are cells 2 b having the opposite orientation in the axialdirection, viz. the arrow-head or heart point in the opposite direction.

The tubular body is cylindrical in the unloaded state, and consequentlyall the annular rows, including the annular end row of cells are capableof expanding into contact with the vascular wall, and preferably theannular end row has the same diameter as the subsequent rows when thetubular body is in the unloaded state, but it can alternatively alsohave a larger diameter than the subsequent annular row.

Each cell 2 a has two first cell sides 3 converging towards one anotherto become mutually connected in an area of interconnection 8 between thecells 2 a in one row and the cells 2 a in the subsequent annular row.The first cell sides 3 form at either end side of the annular row ofcells a circumferentially closed loop 20 in which the first cell sidesextend at an angle α of approx. 107° with respect to the axial directionA. On the side facing the area of interconnection the two first cellsides 3 extending from the area of interconnection 8 consequently forman angle δ=360°−2×α=146°. Each cell 2 a also has two mutually convergingsecond cell sides 4 converging towards one another to become mutuallyconnected in connections 7 between the cells 2 a in the annular row. Thesecond cell sides 4 interconnect the loops 20 at either side of theannular row of cells 2 a. The second cell sides 4 extend in directionsforming an angle β of approx. 38° with respect to the axial direction A.In other embodiments the mentioned angles can take other values. Theangle α can e.g. be in the range from 60° to 120°, and the angle β cane.g. be in the range from 20° to 70°. Preferably the angle δ is lessthan 180°, and suitably less than 176°.

The cell sides 3 are positioned opposite to cell sides 4 of the samecell, and the cells 2 a of each cell row are connected by means ofconnections 7 forming loop-shaped nodes. The areas of interconnection 8interconnecting one annular row of cells with the next row of cells forma node made up by wires wound once around each other. In the embodimentshown, the connections 7 and areas of interconnection 8 are mutuallycircumferentially offset with a distance corresponding substantially tothe circumferential extent of one of the cell sides 3.

FIG. 2 depicts the tubular body 1 of the stent. An engagement member 9is attached to an end row 12 of cells located at the left end of tubularbody 1. The engagement member 9 is formed by four tie members in theform of wire sections, which are connected to each other at a junction10 located at the longitudinal central axis of the tubular body 1. Theindividual tie member is connected to the tubular body 1 at anattachment points 11, the attachment points 11 being circumferentiallyoffset with respect to the connections 7 at the end of the tubular body1 with a distance corresponding substantially to the circumferentialextent of one of the first cell sides 3. This locates each individualattachment point 11 at the middle of the cells 2 a between the twoadjacent connections 7 in the annular row 12 of cells at the end of thetubular member 1. The tie members have a length so that the junction 10is located approximately 1.0×W away from the loop of the end row 12 ofcells at the end of the tubular body 1, W being the width of one row ofcells in the axial direction of the tubular body. There is preferablyone tie member extending from each attachment point to the centraljunction 10, and preferably each cell in the annular end row of cellshas one attachment point.

FIG. 3 a to 3 d show sequential steps of the stent of FIG. 2 beingpulled into a tubular member 13 of a retrieval system according to theinvention. A retrieval member 14 is located displaceable within thelumen of the tubular member 13 and has a longer length than the tubularmember so that it can extend out of both the distal end and also out ofthe proximal end wherefrom it can be manipulated. The retrieval memberis provided with an engagement means in the form of a hook 15 at itsdistal end. The retrieval member is e.g. made of steel or anothermaterial of sufficient strength.

The tubular member 13 terminates at its distal end in a distal endopening surrounded by an annular end surface 16 on the tubular member.In the illustrated embodiment the diameter of the tubular member 16corresponds to approximately 55% of the initial diameter of the tubularbody 1 when the latter is in the unloaded (relaxed) state.

In FIG. 3 a the retrieval member 14 of the retrieval system has engagedthe tie members of the engagement member 9 at the junction 10 by meansof the hook 15 being hooked around tie members. In the illustration theengagement member has been pulled towards the tubular member to theposition in which the tie members abut the annular end surface 16 of thetubular member 13. The tubular body 1 is seen to still remain in itsunloaded state.

FIG. 3 b to 3 e show how the third row of cells is pulled into thetubular member 13. In FIG. 3 b the hook 15 has pulled the engagementmember 9 and two rows of cells into the tubular member 13 of theretrieval system, and the loop 20 at the proximal side of the thirdannular row of cells is located at the annular opening. The areas ofinterconnection 8 interconnecting the second and third rows of cellshave been pulled inwards toward the central axis of the tubular body 1and have just passed by the annular end surface 16 and entered the endopening of the tubular member 13. It is the second cell sides 4 of thesecond row of cells that have pulled the areas of interconnection of thesecond row of cells inwards towards the central axis of the tubular body1, bending the first cell sides 3 of the third row of cells inwards.

As can be seen from the illustration in FIG. 3 b, the second cell sides4 of the third row of cells are slightly deformed. Thus, further pullingin the retrieval member 14 causes the first cell sides 3 and theconnections 7 of the third row of cells to be radially drawn down to andpass in through the end opening of the tubular member 13, see FIGS. 3 cand 3 d. It should be noted that in FIGS. 3 b to 3 d the fourth row ofcells remains unaffected of the collapse of the third row of cells andthus has not begun to collapse.

Once the connections 7 in the loop 20 at the proximal side of the thirdannular row have been drawn into the distal end opening of the tubularmember, tubular body 13 can be displaced to the right hand side of thefigure, viz. in direction of the tubular body. During this displacementof the tubular member the second cell sides 4 in the third annular roware moved into the lumen of the tubular member under concurrentdiminishing of the diameter of the cells to correspond to the lumen.

In FIG. 3 e the tubular member has been advanced to be positioned withthe distal end opening located near the proximal end loop 20 of thefourth annular row of cells, the first cell sides 3 of the fourth row ofcells are bending inwards and are starting to pull the fourth row ofcells into the tubular member 13. The process illustrated in FIGS. 3 bto 3 e with respect to the third row of cells is then repeated for thefourth row of cells, and similarly so forth for the subsequent rows ofcells until the entire stent is located inside the tubular member.

In FIG. 4 the initial collapse of the fourth row of cells is elaborated,the illustration showing a cross section along the line IV-IV of FIG. 3e viewed from the left of FIG. 3 e. In FIG. 4 the first cell sides 3 ofthe proximal loop in the fourth row of cells are partially collapsed andextend from the areas of interconnection 8 inside the tubular member 13and outwards to the connections 7. The first cell sides 3 of the fourthrow of cells have been bend to form curved shapes forming a flower-likeshape with four leaves. The fifth row of cells is still in its initialstate, and the first cell sides 3 of the fifth row of cells extend alongthe contours of the larger outer circle of the illustration.

The engagement member on the stent can take other forms than the oneillustrated in the above. It can e.g. be embodied in the form of severalwires crossing each other, so that the junction 10 is formed of thewires inter-crossing one another, but the tie members are preferablyjoined at the junction, in particular if they are of a flexiblematerial. The tie members can be embodied as flexible threads, or theycan be embodied as loops or eyes or legs extending from thecircumference of the end annular row of cells and radially or obliquelyinwards towards the centre line of the tubular body. Preferably, onlyone tie member extends from the junction to the individual attachmentpoint, but one or more of the attachment points can be connected to morethan one tie member. The engagement member can comprise a magnet ormagnetic material. The engagement means on the retrieval member can alsobe shaped with several hooks or it can include a gripper means, atongue, an eye or a string to be fixed to the one or several engagementmembers on the tubular body. What matters is that the engagement meanscan be brought into a condition where the retrieval member can act witha pulling force distributed to the engagement points on the individualcells in the annular end row of the tubular body.

The length of the tie members can depart from the above mentioned lengthcausing the junction 10 to be located approximately 1.0×W away from theloop of the end row 12. In one embodiment the length of the tie memberscorrespond to half the diameter of the tubular body which causes the tiemembers to be radially directed towards the junction, but preferably thetie members are substantially longer. The tie members can also bepre-shaped to locate the junction asymmetrically with respect to thelongitudinal central axis of the tubular body when there is no pull inthe junction and of sufficient flexible construction to allow thejunction to be centred once the engagement means establishes the pull inthe engagement means. This embodiment can be advantageous when it isimportant to maintain the largest possible unobstructed flow areathrough the tubular body during the temporary placement thereof in thevascular vessel. In an embodiment where the tie members are of flexiblethread of having an individual thread length of more than 1.0×W the tiemembers can be folded and temporarily mounted in a storage position onthe end of the tubular body so that approximately the full lumen of thetubular body is unobstructed during the placement in the vascularvessel. When the stent is to be retrieved it is then required to loosenthe folded up tie members so that they are only attached to the tubularbody at the attachment points, before the engagement means can bebrought in proper engagement with the engagement member.

FIG. 5 illustrates another embodiment of a stent according to theinvention made by laser cutting or etching of a tubular member, thestent being in an unfolded state corresponding to FIG. 1 for the sake ofillustration. In FIG. 5, parts similar to the previous illustrationshave been given similar numerals. The operation of the embodiment ofFIG. 5 corresponds substantially to the previously described embodiment.Thus, in the embodiment of FIG. 5 the connections 7 between the cells 2a, 2 b and the points 8 of interconnection interconnecting subsequentrows of cells are formed as S-shaped joints. This makes said connections7 and said interconnections 8 behave substantially similarly to thepreviously described embodiment. The cells in the tubular body can be ofothers cell patterns than the ones described. The cell sides can e.g.have an undulating run and they can have unequal widths or a widthvarying along the length of the cell side.

The number of cells in the individual annular rows of cells can varydepending on the actual cell shape and the diameter of the tubular bodyin its unloaded state. To give an example there can be four cells ofeven orientation in the annular row, but there can also be three cellsor more than four, such as five, six or seven cells of the sameorientation. Preferably the number of attachment points corresponds tothe number of cells, and more preferably the number of tie memberscorresponds to the number of attachment points. However, if e.g. one ormore of the cells are of weak or more open construction in comparison tothe other cells it is possible to omit the attachment point on the weakcell.

The diameter of the tubular body in the unloaded state vary with theapplication of the stent. For use in arteries the stent can e.g. have adiameter in the range of 0.5 mm to 3 mm when it is to be placed indiminutive arteries or venes, such as in the brain, it can have adiameter in the range of 2 mm to 4 mm for coronary use or pancreaticuses, it can have a diameter in the range from 6 mm to 12 mm for iliac,femoral, renal and carotid uses etc.

The stent can also be provided with a covering on a part of or on thecomplete peripheral surface of the tubular body. The stent can be madeof nitinol thread, such as a round or flat thread, or it can be ofstainless steel, titanium, tantalum, platinum, composite materials or ofsynthetic materials.

In an embodiment the stent is provided with a bioactive material, suchas heparin or another thrombin inhibitor, anti-inflammatory steroidsincluding but not limited to dexamethasone and its derivatives, andmixtures of heparin and such steroids. The bioactive material or agentcan also be an antiproliferative agent such as methotrexate. The stentcan e.g. be placed in the arterial supply of the tumor to provide ameans of delivering a relatively high dose of the antiproliferativeagent directly to the tumor. The bioactive material can furthermore be avasodilator such as a calcium channel blocker or a nitrate. The stentcan also be provided with a drug, such as an anti-cancerchemotherapeutic agent for delivery to a localized tumor, e.g. tamoxifencitrate, Taxol or derivatives thereof. Proscar®, Hytrin®, or Eulexin®.Dopamine or a dopamine agonist such as bromocriptine mesylate orpergolide mesylate can be mentioned as examples of drugs for otherpurposes. The stent can also be provided with a factor that exhibitanti-proliferative activity against cells. Such factors or compositionscan e.g. be a cytotoxic/cytostatic, anti-proliferative factor. Apharmaceutically acceptable form of an anti-proliferative factor or afunctional analog thereof can typically be used.

Details of the above mentioned embodiments can be combined into otherembodiments within the scope of the appended claims. The cell shapesneed not be of the particular type illustrated on the drawing, as thescope of the claims comprises other cell shapes, such as approximatelyrectangular cells, cells where the connections between the cells in theindividual row of cells extend mainly or completely in the axialdirection of the tubular body and the cell sides (the abovementionedfirst cell sides) forming circumferentially closed loops extend indirections forming angles of at least 92° or less that 88° with theaxial direction of the tubular body. The cells can also be polygonal,such as hexagonal, or the first cell sides in the circumferentiallyclosed loops can have a wavy shape or form a meander shape.

1. Stent and stent retrieval system, said retrieval system comprising atubular member with a lumen terminating in a distal end opening, and aretrieval member with a least one engagement means, the tubular memberand the retrieval member being mutually axially displaceable while theretrieval member extends in said lumen of the tubular member, said stentcomprising at least one engagement member to which said at least oneengagement means can engage and a tubular body of a plurality of annularrows of cells that are interconnected and located one after the other inthe axial direction of the tubular body, the cells in one annular row ofcells being interconnected with the subsequent row of similarly orientedcells at areas of interconnection which in said subsequent annular rowof cells are circumferentially offset with respect to the connectionsbetween the cells in said subsequent annular row of cells, wherein theend row of cells is an annular row of cells comprising first cell sidesforming at least one circumferentially closed loop in which theindividual cell has an attachment point, wherein said at least oneengagement member comprises at least three tie members that are mutuallyconnected at a junction and extend individually from the junction to theattachment point of an associated cell, and wherein the attachmentpoints in the annular end row of cells are circumferentially offset withrespect to the connections or areas of interconnection at the end of thetubular body between the cells in said end row.
 2. Stent and stentretrieval system according to claim 1, wherein the individual attachmentpoint is circumferentially located approximately at the middle betweenthe two adjacent connections or areas of interconnection.
 3. Stent andstent retrieval system according to claim 1, wherein the individual areaof interconnection is circumferentially located approximately at themiddle between the two adjacent connections.
 4. Stent and stentretrieval system according to claim 1, wherein the first cell sidesextending from the individual attachment point form mutually on the sideof the attachment point an angle (δ) of less than 176°.
 5. Stent andstent retrieval system according to claim 1, wherein in the individualannular rows of cells located within the tubular body the first cellsides form at least one circumferentially closed loop in which the firstcell sides extending from the individual area of interconnection formmutually on the side facing the end row with the attachment points anangle (δ) of less than 176°.
 6. Stent and stent retrieval systemaccording to claim 1, wherein in the individual annular row of cells thefirst cell sides form at least one circumferentially closed loop inwhich said first cell sides constituting the loop extend in directionsforming angles (α) in the range from 60° to 120°, with the axialdirection (A) of the tubular body, when the tubular body is in anunloaded state.
 7. Stent and stent retrieval system according to claim1, wherein second cell sides in the individual annular row of cellsinterconnect the circumferentially closed loops and extend at leastalong part of their length in directions forming angles (β) in the rangefrom 20° to 70°, with the axial direction (A) of the tubular body, whenthe tubular body is in an unloaded state.
 8. Stent and stent retrievalsystem according to claim 1, wherein said first cell sides extendsubstantially in a radial plane at the distal end opening of the tubularmember, when second cell sides in an adjacent annular row of cells havebeen pulled in through the distal end opening to extend from said distalend opening and into the tubular member.
 9. Stent and stent retrievalsystem according to claim 1, wherein while a loop is pulled into thedistal end opening, the outer diameter of the subsequent loop outsidethe tubular member remains unaffected.
 10. Stent and stent retrievalsystem according to claim 1, wherein said junction is located at thelongitudinal central axis of the tubular body.
 11. Stent and stentretrieval system according to claim 1, wherein the tie members have alength so that the junction is located at least 0.5×W away from theannular end row of cells, W being the width in the axial direction ofthe annular row of cells.
 12. Stent and stent retrieval system to claim1, wherein said at least one engagement member comprises magneticmaterial.
 13. Stent and stent retrieval system according to claim 12,wherein said magnetic material has a polarity which is opposite to thepolarity of a magnetic material located on the engagement means. 14.Stent and stent retrieval system according to claim 1, wherein the innerlumen of the tubular member has a diameter in the range from 20% to 80%of the outer diameter of the tubular body in the unloaded state of thetubular body.
 15. Stent and stent retrieval system according to claim 1,wherein the tubular body is provided with at least one additional meansselected from the group consisting of a medically active substance, abioactive factor inhibiting proliferation of a tumor cell, a bioactivesubstance, a bioactive agent, a drug, and a coating layer for controlledrelease of one or more of a bioactive material, a medically activesubstance or bioactive factor.
 16. Stent and stent retrieval systemaccording to claim 15, wherein said additional means has a predeterminedactive period in the range from three days to one month.
 17. Stent andstent retrieval system according to claim 1, wherein the tubular body isprovided with a tubular covering.
 18. A method of pulling a stent into atubular member, the stent comprising at least one engagement member anda tubular body having a plurality of annular rows of cells that reinterconnected and located one after the other in the axial direction ofthe tubular body, where at least one engagement means grips the at leastone engagement member and pulls it through a distal end opening of thetubular member and into an inner lumen of said tubular member, saidannular rows of cells having an initial diameter which is larger thanthe diameter of said inner lumen, further comprising pulling said atleast one engagement member into and along the lumen of the tubularmember and pushing the tubular member towards the tubular body, wherebythe annular rows of cells maintain their initial diameter at least untilthey are within one row from said end opening.
 19. A method of pulling astent into a tubular member according to claim 18, wherein when theengagement member is pulled, each cell in the annular end row of cellsis pulled towards the lumen of the tubular member by a tie member of theengagement member, said engagement member comprising a plurality of tiemembers for simultaneously pulling all cells in the annular end row downto a reduced diameter at said end opening.